The present invention relates to a method for forming infrared reflection films used for light sources such as incandescent lamps or tungsten-halogen lamps. The present invention relates also highly efficient light sources as light bulbs provided with the infrared reflection films.
xe2x80x98Journal of Illuminating Engineering Societyxe2x80x99, Jul. 1980 (p.197-203) or some other documents have suggested methods for providing low power incandescent lamps and tungsten-halogen lamps. For this purpose, light bulbs are coated with infrared reflection films to substantially pass only visible light that is selected from light beams emitted from filament portions of the light bulbs.
In this method, a maximum proportion of the infrared reflection light, which appears to compose 70-80% of the radiation energy, can be reflected inside of the light bulb. The reflected light is focused on the filament coil portion to heat the same portion. Since the filament coil portion is re-heated in this manner, the consumed power is reduced by 20-30% in comparison with a conventional light bulb when the illuminance (total value of luminous flux) from the filament portions is equivalent.
Such an infrared reflection film includes an interference multilayer film having a laminate of transparent dielectric thin films with high refractive index and low refractive index. The interference multilayer film decreases infrared rays escaping as heat rays from the light bulb, and it selectively passes visible light only, so that the infrared rays can be reflected effectively.
To form infrared reflection films with the best uniformity on three-dimensional objects (in many cases, spheroids) such as light bulbs, various methods such as CVD, evaporation or sputtering are used.
In the above-mentioned interference multilayer films, the films are required to be coated with an accurate thickness while they have desired refractive indices. Evaporation and sputtering are useful in forming thin films with a controlled thickness on conventional flat substrates. However, the methods are not suitable for forming thin films with a uniform thickness on three-dimensional objects including spheroids such as light bulbs.
In a case of a three-dimensional object, generally, the distance from the object to either an evaporation source or a sputtering target can vary. Moreover, the other side (the side away from the evaporation source or the target) of the object should be also coated with a film. As a result, the film has a considerably uneven thickness, and the multilayer film cannot show its functions, and the efficiency of the infrared ray reflection will deteriorate.
Furthermore, visible light of a wavelength to be transmitted is reflected excessively due to the film with uneven thickness. As a result, problems such as coloration and color unevenness will occur in the electric light source.
CVD is used for forming thin films by using starting molecules which are supplied as a gas flow from substantially all directions rather than a specific direction. This method can provide comparatively uniform film thickness without any special difficulties. However, CVD also presents several problems, for example, the absolute value of the film thickness cannot be controlled sufficiently. In addition, the object will be heated inevitably, and the material gasses or the conditions should be changed for the respective films composing a laminate.
To solve the problems, the present invention provides a method for forming thin films with a uniform thickness on substrates including spheroids even by film-forming methods such as evaporation or sputtering. In evaporation or sputtering, incident particles as film materials will be supplied from a specific direction. The present invention also provides a spheroid coated with a film of the method, a light bulb including the spheroid and equipment for film formation.
In order to achieve the purpose, the method for forming thin films according to the present invention includes forming a thin film on a substrate including a spheroid with an incident particle beam coming from a particle source located in a specific direction when viewed from the substrate. In this method, a spin motion and a swing motion are performed together. The spin motion is a rotation of the substrate at a constant angular velocity about the spheroidal axis. Here, xe2x80x98spheroidal axisxe2x80x99 refers to the central axis of the rotation of a spheroid. The swing motion is a rotational oscillation of the same substrate for rotationally oscillating the axis at a constant cycle in one surface, where the center of the rotational oscillation is in the vicinity of the midpoint between two focal points on the axis of the spheroid.
In the method using a spin motion and a swing motion together, a thin film that has a uniform thickness in the peripheral direction of the substrate and in the rotational direction of the spin motion can be formed even if the substrate comprises a spheroid.
It is preferable in the method that the swing motion is performed to get the part of the substrate below the midpoint of the axis positioned away from the particle source when the upper part of the same axis approaches the particle source, so that the uniformity of the thin film in the rotational axis direction is further assured.
It is also preferable that the particle source is a flat plate and the swing motion is performed to rotationally oscillate the axis at a constant cycle in a surface perpendicular to the flat plate surface, so that the uniformity of the thin film in the rotational axis direction is further assured.
It is preferable that the rotational angular velocity of the rotational oscillation of the swing motion is varied continuously, so that the rotational velocity of the swing motion can be set to be suitable for the distance distribution between the substrate surface and the particle source surface.
It is preferable that the rotational oscillation is varied intermittently by setting plural stationary positions within the rotational oscillation range and also stationary times at the respective positions, so that the swing motion can be performed easily.
It is preferable that the thin film is formed by either sputtering or evaporation.
It is preferable that the thin film is at least one selected from the group consisting of an infrared reflection film and a frost film.
It is also preferable that the substrate including a spheroid is a light bulb.
It is preferable that the center of the rotational oscillation of the swing motion is in the vicinity of the longitudinal center of the filament portion of the light bulb.
A spheroid of the present invention is coated with a thin film, and the thin film is formed with an incident particle beam coming from a particle source located in a specific direction when viewed from the spheroid as an object. The spheroid is subjected to a spin motion together with a swing motion in order to form a thin film thereon. The spin motion is a rotation of the spheroid at a constant angular velocity about the spheroidal axis. The swing motion is a rotational oscillation of the same spheroid for rotationally oscillating the axis at a constant cycle in one surface, where the center of the rotational oscillation is in the vicinity of the midpoint between two focal points on the axis of the spheroid. The thin film has a uniform thickness at least in the rotational direction of the spin motion and also in the rotational oscillation direction of the swing motion.
The spheroid coated with the thin film is useful for light bulbs due to the uniformity in the film thickness.
It is preferable in the spheroid that the swing motion is performed to get the part of the spheroid below the midpoint of the axis positioned away from the particle source when the upper part of the same axis approaches the particle source, so that the uniformity of the thin film in the rotational axis direction is further assured.
It is also preferable that the particle source is a flat plate and the swing motion is performed to rotationally oscillate the axis at a constant cycle in a surface perpendicular to the flat plate surface, so that the uniformity of the thin film in the rotational axis direction is further assured.
It is preferable that the thin film is formed by sputtering or by evaporation.
It is also preferable that the thin film is at least one selected from the group consisting of an infrared reflection film and a frost film.
It is preferable that the spheroid is a light bulb.
It is preferable that the center of the rotational oscillation of the swing motion is in the vicinity of the longitudinal center of the filament portion of the light bulb.
A light bulb of the present invention includes a spheroid coated with a thin film. The film on the light bulb is substantially uniform in thickness, since it is formed with an incident particle beam coming from a specific direction while the spheroid (light bulb) is subjected to a swing motion together with a spin motion. In order to meet the requirement for the uniformity, the film thickness on the spheroidal substrate in a range of xc2x160xc2x0 from the vertical angle (see the upper right-hand in the graph of FIG. 1) is at least 88% of the maximum film thickness, i.e., xc2x16% to the medium value. When the thin film is a laminate comprising transparent dielectric thin films differing in their refractive indices, the light bulb can be prevented from being colored or having color unevenness, and the energy will be saved considerably.
Film-formation equipment of the present invention is used to form thin films having a uniform thickness on substrates comprising spheroids with an incident particle beam coming. from a particle source located in a specific direction when viewed from the substrates. The equipment is provided with a rotational mechanism to perform a spin motion together with a swing motion. The spin motion is a rotation of the spheroid at a constant angular velocity about the spheroidal axis. The swing motion is a rotational oscillation of the same spheroid for rotationally oscillating the axis at a constant cycle in one surface, where the center of the rotational oscillation is in the vicinity of the midpoint between two focal points on the axis of the spheroid.
It is preferable that the equipment uses RF (radio frequency) sputtering or DC (direct current) sputtering in the film formation process.